Newton’s Cannonball

Newton was interested in two aspects of the Moon’s orbit:

1) Why, if all objects feel the acceleration due to gravity toward the Earth, doesn’t the Moon come crashing out of the sky and onto Earth?

and

2) Why, if as Galileo said, objects move with constant speed and direction until acted upon by an external force, does the Moon move in a circle rather than a straight line?

Newton’s cannonball was a thought experiment Isaac Newton used to hypothesize that the force of gravity was universal, and it was the key force for planetary motion. Learn how he uses a cannon to solve these questions.